The invention relates to improvements in couplings for plain end pipes, and more particularly to improvements in pipe couplings of the type wherein a tubular housing has two flange-like end portions each of which surrounds the plain end of one of the pipes and the housing contains two sets of toothed blocking elements which are rotatable in response to axial movement of at least one of the pipes away from the other pipe and serve to oppose separation of the pipes.
German Pat. No. 24 28 101 discloses a pipe coupling wherein the plain ends of the pipes are surrounded by a tubular housing having two flange-like end portions which extend radially inwardly toward the peripheries of the respective pipes. The coupling further comprises two blocking devices each of which surrounds the end of one of the pipes and is disposed in the interior of the housing. Each blocking device has several claws which penetrate into the peripheral surfaces of the respective pipes when the pipes are moved axially and away from each other. The blocking devices have rings with a substantially frustoconical cross sectional outline, and the rings are tiltable in the interior of the housing. That marginal portion of each ring which has a relatively small diameter is provided with axially extending slots to form laminations constituting the aforementioned claws. The neighboring laminations overlap each other and can penetrate into the material of the adjacent pipe end in response to movement of the pipes away from each other. The conical portion of each ring changes its angular position in response to a pull upon one of the pipes so that the claws penetrate into the material of the pipes and tend to prevent further axial displacement of the pipes away from each other. A drawback of the patented blocking device is that the entire material of each ring must be deformed in order to change the angular positions of the rings in the housing. This necessitates the exertion of a substantial bending moment and, as a rule, a substantial axial displacement of at least one of the pipes before the blocking devices become effective. The force which causes the rings to change their angular positions becomes effective only when substantial quantities of the material of the pipes accumulate in front of the respective claws.
U.S. Pat. No. 1,930,194 to Dillon discloses a pipe coupling wherein the blocking elements constitute substantially segment-shaped parts which are tiltable in the interior of the housing of the coupling between two spaced-apart angular positions determined by the internal surfaces of the adjacent portions of the housing. Each set of segment-shaped blocking elements is tiltable about a fixed axis defined by a ring-shaped shaft which is mounted in the housing. Those portions of the blocking elements which are adjacent to the peripheral surfaces of the respective pipes have teeth which penetrate into the adjacent material in response to a pull upon the pipes in a direction to move them apart. The teeth are provided on circular surfaces having their centers on the respective ring-shaped shafts. A drawback of the patented pipe coupling is that the force with which the blocking elements hold the pipes against separation does not increase, or decreases only insignificantly, in response to a pull upon the one or the other pipe in a direction to separate the pipes from each other.
U.S. Pat. No. 2,005,056 to Stephens discloses a pipe coupling wherein the blocking elements are rollers having circumferentially extending teeth and being rotatable about axes which are parallel to the common axis of the pipes. The patentee states that the roller-shaped blocking elements are sluggishly rotatable in response to the application of a force tending to separate the pipes from each other. Such sluggish rotatability does not prevent pronounced axial movements of the pipes away from each other.
British Pat. No. 1,112,605 to Barr discloses a pipe coupling wherein the housing of the coupling confines a ring-shaped rubber body with wires incorporated therein. The pipes which are to be coupled to each other are inserted into one another, and a single rubber body is placed between the external surface of the inserted pipe and the internal surface of the surrounding pipe. The rubber body performs the function of a seal. The pipes which are to be coupled by the rubber body must be provided with internal and external grooves for reception of portions of the rubber body.
U.S. Pat. No. 2,182,797 to Dillon discloses a further pipe coupling which comprises sprag-like blocking elements disposed between a surrounding pipe and a surrounded pipe and being active only as long as one of the pipes is pulled axially away from the other pipe. The sprags resemble spheres and are unlikely to invariably oppose axial movements of the two pipes away from each other. Such sprags must be inserted into specially configurated internal grooves of the outer pipe. The patented coupling is expensive and unreliable, especially if the pipes which are coupled to each other are not continuously stressed in a direction to move axially and away from each other.